Cooling medium for data center and preparation method thereof

Abstract

The invention relates to the technical field of cooling media, in particular to a cooling medium for a data center and a preparation method of the cooling medium. A basic solution is formed by compounding a bio-based poly-alpha-olefin-polycaprolactone block copolymer and polyethylene glycol monomethyl ether; the modified magnetic-loaded boron nitride nanosheet is prepared by compounding a boron nitride nanosheet and ferroferric oxide and then coating a polydopamine-chitosan coating, the phase change microcapsule is prepared by taking graphene quantum dots as a heat conduction modifier, and the other components are prepared by a corresponding modification or polymerization process. According to the compound basic liquid, environmental protection and high and low temperature adaptability are both considered, the problems of agglomeration and leakage are solved through the modified nanoparticles and the phase change microcapsules, multiple guarantees such as oxidation resistance and corrosion inhibition are achieved through cooperation of the auxiliaries, the service life of a cooling medium is prolonged, and the maintenance cost is reduced.

Description

Technical Field

[0001] This invention relates to the field of cooling medium technology, specifically to a cooling medium for data centers and its preparation method. Background Technology

[0002] With the rapid development of the digital economy, the demand for computing power in data centers is growing exponentially, and the power density of server clusters continues to rise. Cooling systems have become a core component in ensuring the stable operation of data centers and controlling energy consumption. Among the current mainstream cooling technologies, liquid cooling is gradually replacing traditional air cooling as the preferred solution for high-density data centers due to its advantages such as high heat exchange efficiency and low energy consumption. The performance of the cooling medium directly determines the heat exchange efficiency, equipment compatibility, and long-term operational stability of the cooling system.

[0003] Current data center cooling media are mainly classified into three categories: mineral oil, synthetic esters, and water-based coolants. Mineral oil-based media are low-cost and have excellent insulation properties, but they have poor biodegradability and are prone to oxidative cracking and sludge formation with long-term use. They also have poor low-temperature fluidity, requiring additional heating in cold regions or low-temperature conditions, increasing energy consumption. While synthetic ester-based media have improved biodegradability, their high-temperature oxidation resistance is weak, and long-term cyclic use can lead to increased viscosity and acid value. Furthermore, their thermal conductivity is generally low, requiring the addition of thermally conductive fillers to improve performance. Water-based coolants have high thermal conductivity and are inexpensive, but their poor insulation properties can easily cause short circuits in server hardware. They also require the addition of large amounts of corrosion inhibitors and scale inhibitors, and long-term use can lead to corrosion and scaling problems. In low-temperature environments, they are prone to freezing and expansion, damaging cooling pipes.

[0004] To improve the overall performance of cooling media, the industry has attempted to optimize formulations through composite modification. For example, adding boron nitride, graphene, and other nano-thermal conductive particles to the base fluid can increase thermal conductivity. However, nanoparticles have a large specific surface area and exhibit severe agglomeration, making long-term stable dispersion difficult even with the addition of dispersants, easily leading to pipe blockage and reduced heat exchange efficiency. Furthermore, some solutions introduce phase change materials to enhance heat storage capacity; however, traditional phase change materials suffer from leakage, phase separation, and low thermal conductivity, limiting their application in cooling media. Simultaneously, existing cooling media lack sufficient synergistic optimization in areas such as hydrolysis resistance, antibacterial properties, and long-term stability, failing to meet the stringent requirements of data center cooling systems for long media lifespan and low maintenance costs. Therefore, developing a cooling medium that combines high thermal conductivity, high stability, excellent biodegradability, and comprehensive functional guarantees has become a key breakthrough direction for the development of data center liquid cooling technology. Summary of the Invention

[0005] (a) Technical problems to be solved To address the shortcomings of existing technologies, this invention provides a cooling medium for data centers and a method for preparing the same.

[0006] (II) Technical Solution A cooling medium for data centers comprises the following components in parts by weight: 50-70 parts of bio-based polyα-olefin-polycaprolactone block copolymer, 20-30 parts of polyethylene glycol monomethyl ether, 1-5 parts of polydopamine-chitosan composite-coated modified magnetic boron nitride nanosheets, 3-7 parts of graphene quantum dot-doped n-octadecane@polyurea-polyacrylate double-shell hollow phase change microcapsules, 0.6-1 part of polymethyl methacrylate-polyethylene glycol block copolymer, 0.2-0.6 parts of hexadecyltrimethylammonium chloride-modified montmorillonite, 0.2-0.6 parts of antioxidant 2,6-di-tert-butyl-p-cresol, 0.2 parts of corrosion inhibitor benzotriazole, 0.1 parts of antibacterial agent isothiazolinone, and 0.2 parts of antihydrolysis agent polycarbodiimide; The bio-based polyalphaolefin-polycaprolactone block copolymer was prepared by catalytic ring-opening polymerization of caprolactone at 130°C using hydroxyl-terminated bio-based polyalphaolefin as an initiator and stannous octoate as a catalyst. The magnetically loaded boron nitride nanosheets modified with polydopamine-chitosan composite coating were prepared by sol-gel method using boron nitride nanosheets and iron oxide particles, and then coated with polydopamine-chitosan composite coating. The graphene quantum dot-doped n-octadecane@polyurea-polyacrylate double-shell hollow phase change microcapsules were prepared by suspension polymerization-interfacial polymerization using graphene quantum dots prepared by sodium citrate pyrolysis as thermal conductivity modifier. The modified montmorillonite was ion-exchange modified with a 5% (w / w) hexadecyltrimethylammonium chloride solution. The polymethyl methacrylate-polyethylene glycol block copolymer was prepared by atom transfer radical polymerization.

[0007] Preferably, the bio-based poly-α-olefin-polycaprolactone block copolymer has a number-average molecular weight of 900, a poly-α-olefin block ratio of 3:2 to polycaprolactone block ratio, a viscosity of 30 mm² / s at 40°C, and a molecular weight distribution of 1.2. The polymerization reaction is carried out under nitrogen protection. After the reaction is completed, unreacted monomers are removed by vacuum distillation, with the vacuum degree controlled at 0.09 MPa and the temperature at 120°C. The amount of stannous octoate used is 0.5% of the total mass of the monomers. After cooling, a pale yellow, transparent, viscous liquid is obtained.

[0008] Preferably, the preparation process of the polydopamine-chitosan composite coating modified magnetically loaded boron nitride nanosheets is as follows: magnetically loaded boron nitride nanosheets are ultrasonically dispersed in Tris-HCl buffer solution, dopamine hydrochloride is added, the pH is adjusted to 8.5, the reaction is stirred to form a polydopamine coating, then 1 wt% chitosan hydrochloride solution is added, the reaction is continued, and after completion, the nanosheets are washed with deionized water and vacuum dried; the boron nitride nanosheets have a thickness of 15 nm and a lateral dimension of 80 nm, the polydopamine-chitosan composite coating has a thickness of 5 nm, the chitosan has a degree of deacetylation of 90%, a number-average molecular weight of 20,000, a thermal conductivity of 850 W / (m·K), and a saturation magnetization of 12 emu / g.

[0009] Preferably, in the preparation of the graphene quantum dot-doped n-octadecane@polyurea-polyacrylate double-shell hollow phase change microcapsules, n-octadecane and graphene quantum dots are mixed uniformly at 50°C and 800 rpm for 30 min. The oil phase consists of n-octadecane, graphene quantum dots, pore-forming agent and acrylate monomer. The aqueous phase is a 2.5 wt% OP-10 aqueous solution. The mass ratio of oil phase to aqueous phase is 1:4. The suspension polymerization temperature is 70°C and the time is 2.5 hours. During interfacial polymerization, the molar ratio of hexamethylene diisocyanate to ethylenediamine is 1.2:1, and the reaction temperature is 55°C and the time is 1.5 hours.

[0010] Preferably, in the atom transfer radical polymerization of the polymethyl methacrylate-polyethylene glycol block copolymer, the initiator is ethyl α-bromoisobutyrate, the catalyst is CuBr / tris(2-dimethylaminoethyl)amine in a molar ratio of 1:2, the monomers are methyl methacrylate and polyethylene glycol monomethyl ether acrylate in a molar ratio of 3:2, the polymerization temperature is 70°C, the reaction time is 12 hours, and the product is purified by precipitation with petroleum ether and vacuum drying for 6 hours after the reaction.

[0011] Preferably, the anti-hydrolysis agent polycarbodiimide has a number average molecular weight of 10,000, an isocyanate group content of 12%, and a viscosity of 800 mPa·s at 25°C; the antibacterial agent isothiazolinone is a compound of 5-chloro-2-methyl-4-isothiazolin-3-one and 2-methyl-4-isothiazolin-3-one in a mass ratio of 3:1, with an active ingredient content of 15%.

[0012] Preferably, the method for preparing the cooling medium for the data center includes the following steps: S1: Weigh out the bio-based polyα-olefin-polycaprolactone block copolymer and polyethylene glycol monomethyl ether by weight, add them to a reactor equipped with a stirrer and an ultrasonic device, seal the reactor, and purge with nitrogen three times, each time for 10 minutes at a pressure of 0.1 MPa. Heat the reactor to 50°C, stir at 500 rpm for 50 minutes, and simultaneously apply 200W intermittent ultrasonic treatment for 20 minutes, working for 30 seconds and pausing for 10 seconds. Insert the ultrasonic probe 2 cm below the liquid surface to obtain a clear and transparent premixed base liquid. S2: Add the polydopamine-chitosan composite coating modified magnetic boron nitride nanosheets to the premixed base liquid in step S1, adjust the temperature to 40℃, and use a high shear disperser to shear at 10000rpm for 30min, while simultaneously applying 350W ultrasonic-assisted dispersion with an ultrasonic frequency of 20kHz and an amplitude of 50%, to obtain a dispersion of nano-thermal conductive particles without obvious sedimentation. S3: Add polymethyl methacrylate-polyethylene glycol block copolymer and modified montmorillonite to the dispersion in step S2, heat to 45°C, stir at 600 rpm for 60 min, then transfer to a three-roll mill (model S400). Preheat the mixture to 50°C before grinding. The grinding roller speed ratio is 3:1:5, with the front roller at 20 rpm, the middle roller at 60 rpm, and the rear roller at 100 rpm. The grinding gap is 5 μm. Grind three times in a cycle. After grinding, the particle size D90 is measured using a laser particle size analyzer and is ≤2 μm to obtain a stable dispersion. S4: Add graphene quantum dot-doped n-octadecane@polyurea-polyacrylate double-shell hollow phase change microcapsules, antioxidants, corrosion inhibitors, antibacterial agents, and antihydrolysis agents to the stable dispersion in step S3 in sequence, adjust the temperature to 38℃, stir at 550 rpm for 80 min, and take samples every 20 min to check the dispersion uniformity. S5: The mixture from step S4 is fed into a high-pressure homogenizer, model AH-BASIC, with the inlet temperature controlled at 30℃. It is homogenized twice at a pressure of 70MPa, each time for 6 minutes, and the outlet temperature does not exceed 45℃. After homogenization, it is aged in a constant temperature chamber at 28℃ for 20 hours. During the aging process, it is stirred at 250rpm for 12 minutes every 6 hours. Finally, it is vacuum filtered through a 5μm polytetrafluoroethylene filter membrane at a vacuum degree of 0.08MPa to remove large particulate impurities and obtain the cooling medium.

[0013] Preferably, the stirring paddle in step S1 is an anchor-type stirring paddle with a blade diameter of 2 / 3 of the inner diameter of the reactor. During stirring, it ensures that a stable vortex is formed on the liquid surface, and the vortex depth is 1 / 5 of the liquid surface height.

[0014] Preferably, the roller material of the three-roll mill in step S3 is zirconia ceramic. During the grinding process, the roller temperature is controlled at 40°C by circulating water. After each grinding, a sample is taken for testing. If D90 > 2μm, one more grinding cycle is added.

[0015] Preferably, the homogenizing valve of the high-pressure homogenizer in step S5 is made of tungsten carbide. After homogenization, the dispersion stability is tested by centrifugal sedimentation. The conditions are centrifugation at 3000 rpm for 30 minutes, and the volume ratio of the supernatant is ≥98% to be qualified. The filtered cooling medium is sealed in a polyethylene barrel with nitrogen and stored in the dark.

[0016] (iii) Beneficial technical effects Compared with existing technologies, the beneficial effects of this invention are: 1. The bio-based polyα-olefin-polycaprolactone block copolymer is compounded with polyethylene glycol monomethyl ether, which not only retains the excellent biodegradability of bio-based materials and meets environmental protection requirements, but also achieves a balance between viscosity and flowability through block structure regulation. It takes into account the low viscosity characteristics under high temperature conditions and the flowability under low temperature conditions, without the need for additional heating or cooling adjustment, and has a wider range of applicable environments.

[0017] 2. The polydopamine-chitosan composite coating modified magnetically loaded boron nitride nanosheets effectively solves the problem of agglomeration of traditional nano-thermal conductive particles. The composite coating not only improves the compatibility between the particles and the base liquid, achieving long-term stable dispersion and avoiding the risk of pipeline blockage, but its magnetic loading properties can also assist in the subsequent recovery of the medium. Meanwhile, the graphene quantum dot-doped double-shell hollow phase change microcapsules synergistically improve thermal conductivity and heat storage capacity. The double-shell structure effectively suppresses leakage of the phase change core material, and the hollow design enhances the heat transfer rate during the phase change process, achieving rapid heat absorption and release, and improving the heat exchange stability of the system.

[0018] 3. The synergistic effect of polymethyl methacrylate-polyethylene glycol block copolymer and modified montmorillonite constructs a three-dimensional stable network, further enhancing the dispersion stability of the system and preventing component stratification. The scientific formulation of composite functional additives provides multiple protections including anti-oxidation, corrosion inhibition, antibacterial properties, and hydrolysis resistance, effectively slowing down the oxidative aging rate of the medium, reducing corrosion of metal components, inhibiting microbial growth, preventing sludge and scale formation, significantly extending the service life of the cooling medium, and reducing the maintenance costs of data center cooling systems. Attached Figure Description

[0019] Figure 1 This is a flowchart of a method for preparing a cooling medium for data centers, as disclosed in this invention. Figure 2 This is a histogram comparing the thermal conductivity and dispersion stability of the examples and comparative examples; Figure 3 This is a line graph comparing the phase change thermal storage density and viscosity at 40°C of the examples and comparative examples; Figure 4 This is a radar comparison chart created by standardizing the dimensions of the performance comparison data of the examples and comparative examples. Detailed Implementation

[0020] according to Figures 1 to 4 The specific embodiments of the present invention are as follows: Raw material preparation (a) Basic raw materials Hydroxyl-terminated bio-based polyalphaolefin, number average molecular weight 500; caprolactone monomer; stannous octoate; polyethylene glycol monomethyl ether, number average molecular weight 400; boron nitride nanosheets, thickness 15 nm, lateral dimension 80 nm; iron oxide particles; dopamine hydrochloride; Tris-HCl buffer, concentration 0.05 mol / L; chitosan, degree of deacetylation 90%, number average molecular weight 20000; sodium citrate; n-octadecane; porogen is polyethylene glycol 400; acrylate monomers including methyl methacrylate and butyl acrylate; OP-10 emulsifier; hexamethylene diisocyanate; ethylenediamine; ethyl α-bromoisobutyrate. CuBr; Tris(2-dimethylaminoethyl)amine; Methyl methacrylate; Polyethylene glycol monomethyl ether acrylate, number average molecular weight 500; Montmorillonite ore; Cetyltrimethylammonium chloride; Antioxidant 2,6-di-tert-butyl-p-cresol; Corrosion inhibitor benzotriazole; Antibacterial agent isothiazolinone, a compound of 5-chloro-2-methyl-4-isothiazolin-3-one and 2-methyl-4-isothiazolin-3-one in a mass ratio of 3:1, with an active ingredient content of 15%; Antihydrolysis agent polycarbodiimide, number average molecular weight 10,000, isocyanate group content 12%, viscosity at 25℃ 800 mPa·s; Petroleum ether; Deionized water. All raw materials are of industrial grade purity.

[0021] (II) Equipment Preparation 5L reactor with stirring and ultrasonic devices, high shear disperser, S400 three-roll mill, AH-BASIC high-pressure homogenizer, laser particle size analyzer, centrifugal sedimentation apparatus, vacuum drying oven, vacuum distillation apparatus, ultrasonic disperser, constant temperature stirrer, magnetic separation equipment, thermal conductivity tester, viscometer, corrosion test chamber.

[0022] Preparation of key components (I) Preparation of bio-based polyα-olefin-polycaprolactone block copolymer The feed amounts were calculated based on a polyalphaolefin (PAO) to polycaprolactone (VCL) block ratio of 3:2. 180g of hydroxyl-terminated bio-based PAO, 120g of VCL monomer, and 1.5g of stannous octoate (0.5% of the total monomer mass) were weighed and added to the reactor. The reactor was sealed and purged with nitrogen three times for 10 minutes each time, maintaining a pressure of 0.1 MPa. The temperature was raised to 130°C, and the stirring speed was 300 rpm. The reaction was maintained at this temperature for 8 hours to complete the ring-opening polymerization. After the reaction, the vacuum was adjusted to 0.09 MPa, and the temperature was raised to 120°C. Unreacted monomers were removed by vacuum distillation for 2 hours. The mixture was then allowed to cool naturally to room temperature, yielding a pale yellow, transparent, viscous liquid. The copolymer had a number-average molecular weight of 900, a viscosity of 30 mm² / s at 40°C, and a molecular weight distribution of 1.2.

[0023] (II) Preparation of Polydopamine-Chitosan Composite Coating Modified Magnetically Loaded Boron Nitride Nanosheets Preparation of magnetically loaded boron nitride nanosheets: 10 g of boron nitride nanosheets were added to 500 mL of an ethanol-water solution (ethanol to water volume ratio 1:1). The mixture was ultrasonically dispersed for 30 min at a power of 300 W and a frequency of 20 kHz. 3 g of iron oxide particles were added, and the mixture was stirred until homogeneous. The pH was adjusted to 9.0 with ammonia. The temperature was raised to 60 °C, and the reaction was carried out under constant temperature and stirring for 4 hours. During the reaction, the mixture was ultrasonically dispersed for 5 min every 30 min to prevent agglomeration. After the reaction was completed, the product was separated by magnetic separation, washed 5 times with deionized water, and vacuum dried at 60 °C for 12 hours to obtain magnetically loaded boron nitride nanosheets.

[0024] Composite Coating: 5g of the above-mentioned magnetically loaded boron nitride nanosheets were weighed and ultrasonically dispersed in 500mL Tris-HCl buffer for 30min until the solution was homogeneous and transparent. 2g of dopamine hydrochloride was added, and the pH of the system was adjusted to 8.5 with hydrochloric acid and sodium hydroxide. The reaction was carried out at 30℃ with stirring for 6 hours, during which nitrogen gas was continuously purged for protection, forming a polydopamine coating. Subsequently, 100mL of 1wt% chitosan hydrochloride solution was slowly added dropwise, maintaining the temperature at 30℃, and the reaction was continued with stirring for 4 hours. After the reaction was completed, the product was repeatedly washed with deionized water until the washing solution was neutral, and then vacuum dried at 60℃ for 12 hours to obtain the target product. The composite coating of this product had a thickness of 5nm, a thermal conductivity of 850W / (m・K), and a saturation magnetization of 12emu / g.

[0025] (III) Preparation of graphene quantum dot-doped n-octadecane@polyurea-polyacrylate double-shell hollow phase change microcapsules Preparation of graphene quantum dots: Weigh 5g of sodium citrate, put it into a ceramic crucible, place it in a muffle furnace, pyrolyze it at 500℃ for 2 hours, cool it naturally to room temperature, add 200mL of deionized water, sonicate it for 20min, then dialyze it with a dialysis bag with a molecular weight cutoff of 1000 for 48 hours to remove small molecule impurities, and freeze-dry it to obtain graphene quantum dots.

[0026] Microcapsule preparation: Weigh 20g of n-octadecane, add 0.5g of graphene quantum dots, place in a 50℃ constant temperature stirrer, and stir at 800rpm for 30min until homogeneous. Oil phase preparation: Mix the above mixture with 1g of porogen polyethylene glycol 400, 3g of methyl methacrylate, and 2g of butyl acrylate, and stir until homogeneous. Aqueous phase preparation: Weigh 2.5g of OP-10 emulsifier, add 97.5g of deionized water, and stir to dissolve to obtain a 2.5wt% OP-10 aqueous solution. Add the oil phase to the aqueous phase slowly at a mass ratio of 1:4, and perform suspension polymerization at 70℃ and 600rpm for 2.5 hours. Then add 2.4g of hexamethylene diisocyanate, stir until homogeneous, and then add 1g of ethylenediamine dropwise. The molar ratio of hexamethylene diisocyanate to ethylenediamine is 1.2:1. Adjust the temperature to 55℃ and perform interfacial polymerization for 1.5 hours. After the reaction was completed, the product was separated by centrifugation, washed three times with deionized water, and dried under vacuum at 50°C for 8 hours to obtain double-shell hollow phase change microcapsules.

[0027] (iv) Preparation of polymethyl methacrylate-polyethylene glycol block copolymer Weigh out 0.2 mol of ethyl α-bromoisobutyrate initiator, 0.1 mol of CuBr catalyst, 0.2 mol of tris(2-dimethylaminoethyl)amine (CuBr to tris(2-dimethylaminoethyl)amine molar ratio 1:2), 0.3 mol of methyl methacrylate monomer, and 0.2 mol of polyethylene glycol monomethyl ether acrylate (PEG monomethyl ether acrylate molar ratio 3:2), and add them to a reaction flask. Purge the reaction flask with nitrogen three times, seal it, and heat to 70°C. Stir the mixture at 200 rpm for 12 hours. After the reaction is complete, slowly pour the reaction solution into 5 times its volume of petroleum ether. The product precipitates out; filter and collect the precipitate, then purify it by vacuum drying at 60°C for 6 hours to obtain the target copolymer.

[0028] (V) Preparation of hexadecyltrimethylammonium chloride-modified montmorillonite 10g of raw montmorillonite ore was weighed, pulverized, and passed through a 200-mesh sieve. 190mL of deionized water was added, and the mixture was stirred for 30 minutes to prepare a 5wt% suspension. 200mL of a 5% hexadecyltrimethylammonium chloride solution was added, and the mixture was stirred at 300rpm at a constant temperature of 60℃ for 4 hours for ion exchange modification. After the reaction was complete, the mixture was allowed to stand for 4 hours to precipitate. The supernatant was discarded, and the precipitate was washed with deionized water until no white precipitate was formed upon addition of silver nitrate solution to the washings, indicating no chloride ion residue. The precipitate was then dried at 80℃ for 12 hours, pulverized, and passed through a 100-mesh sieve to obtain modified montmorillonite.

[0029] Example 1 (a) Formula composition (parts by weight) The composition includes: 60 parts of bio-based polyα-olefin-polycaprolactone block copolymer, 25 parts of polyethylene glycol monomethyl ether, 3 parts of polydopamine-chitosan composite coating modified magnetic boron nitride nanosheets, 5 parts of graphene quantum dot-doped n-octadecane@polyurea-polyacrylate double-shell hollow phase change microcapsules, 0.8 parts of polymethyl methacrylate-polyethylene glycol block copolymer, 0.4 parts of hexadecyltrimethylammonium chloride modified montmorillonite, 0.4 parts of antioxidant 2,6-di-tert-butyl-p-cresol, 0.2 parts of corrosion inhibitor benzotriazole, 0.1 parts of antibacterial agent isothiazolinone, and 0.2 parts of antihydrolysis agent polycarbodiimide.

[0030] (II) Preparation steps S1: Preparation of the premixed base liquid: Weigh 60 parts of bio-based polyα-olefin-polycaprolactone block copolymer and 25 parts of polyethylene glycol monomethyl ether according to the formula, and add them to a 5L reactor equipped with an anchor-type stirrer. The diameter of the stirrer blade is 2 / 3 of the inner diameter of the reactor. The reactor is equipped with a stirring and ultrasonic device. After sealing the reactor, purge with nitrogen three times, each time for 10 minutes, maintaining a pressure of 0.1 MPa. Raise the temperature to 50℃, stir at 500 rpm for 50 minutes, and simultaneously apply 200W intermittent ultrasonic treatment for 20 minutes, working for 30 seconds and pausing for 10 seconds. Insert the ultrasonic probe 2 cm below the liquid surface. During stirring, ensure that a stable vortex is formed on the liquid surface, with a vortex depth of 1 / 5 of the liquid surface height, to obtain a clear and transparent premixed base liquid.

[0031] S2: Preparation of nano-thermal conductive particle dispersion. Three parts of polydopamine-chitosan composite coated modified magnetic boron nitride nanosheets were added to the premixed base liquid in step S1. The temperature of the reactor was adjusted to 40℃, and a high-shear disperser was started. The disperser was sheared at 10,000 rpm for 30 min. At the same time, 350W ultrasonic-assisted dispersion was applied with an ultrasonic frequency of 20kHz and an amplitude of 50%. The system status was observed every 5 min during the dispersion process to ensure that there was no obvious particle agglomeration. Finally, a nano-thermal conductive particle dispersion with no obvious sedimentation was obtained.

[0032] S3: Preparation of Stable Dispersion. Add 0.8 parts of polymethyl methacrylate-polyethylene glycol block copolymer and 0.4 parts of modified montmorillonite to the dispersion from step S2. Heat to 45℃ and stir at 600 rpm for 60 min. During this time, observe the liquid every 15 min with a glass rod to ensure the system is homogeneous and free of stratification. Then transfer the mixture to an S400 three-roll mill. Preheat the mixture to 50℃ before milling. The milling rollers are made of zirconia ceramic. Set the milling roller speed ratio to 3:1:5: 20 rpm for the front roller, 60 rpm for the middle roller, and 100 rpm for the rear roller, with a milling gap of 5 μm. Repeat the milling process three times. After each milling, take a sample and use a laser particle size analyzer to check the particle size, ensuring D90 ≤ 2 μm, finally obtaining a stable dispersion.

[0033] S4: Mixing of functional additives. 5 parts of graphene quantum dot-doped n-octadecane@polyurea-polyacrylate double-shell hollow phase change microcapsules, 0.4 parts of antioxidant, 0.2 parts of corrosion inhibitor, 0.1 parts of antibacterial agent, and 0.2 parts of anti-hydrolysis agent were added sequentially to the stable dispersion in step S3. The temperature was adjusted to 38℃, and the mixture was stirred at 550 rpm for 80 min. Samples were taken every 20 min during the process, and the dispersion uniformity was observed using an optical microscope to ensure that there was no obvious agglomeration of functional additives.

[0034] S5: Homogenization, Aging, and Filtration. The mixture from step S4 is passed into an AH-BASIC high-pressure homogenizer. The homogenizing valve is made of tungsten carbide, and the inlet temperature is controlled at 30℃. Homogenization is performed twice at 70MPa pressure, 6 minutes each time, with the outlet temperature strictly controlled not to exceed 45℃. After homogenization, the mixture is transferred to a 28℃ constant temperature chamber for 20 hours of static aging. During aging, the mixture is stirred at 250rpm for 12 minutes every 6 hours to prevent component sedimentation. Finally, it is vacuum filtered through a 5μm polytetrafluoroethylene filter membrane at a vacuum level of 0.08MPa to remove large particulate impurities from the system, yielding the finished cooling medium. This product is then sealed in a polyethylene drum under nitrogen and stored away from light.

[0035] Example 2 (a) Formula composition (parts by weight) 50 parts of bio-based polyα-olefin-polycaprolactone block copolymer, 20 parts of polyethylene glycol monomethyl ether, 1 part of polydopamine-chitosan composite coating modified magnetic boron nitride nanosheets, 3 parts of graphene quantum dot doped n-octadecane@polyurea-polyacrylate double-shell hollow phase change microcapsules, 0.6 parts of polymethyl methacrylate-polyethylene glycol block copolymer, 0.2 parts of hexadecyltrimethylammonium chloride modified montmorillonite, 0.2 parts of antioxidant 2,6-di-tert-butyl-p-cresol, 0.2 parts of corrosion inhibitor benzotriazole, 0.1 parts of antibacterial agent isothiazolinone, and 0.2 parts of antihydrolysis agent polycarbodiimide.

[0036] (II) Preparation steps S1: Preparation of Premixed Base Liquid Weigh 50 parts of bio-based polyα-olefin-polycaprolactone block copolymer and 20 parts of polyethylene glycol monomethyl ether, and add them to a 5L reactor equipped with an anchor-type stirrer (the stirrer diameter is 2 / 3 of the reactor's inner diameter). The reactor is equipped with a stirrer and an ultrasonic device. After sealing the reactor, purge with nitrogen three times, each time for 10 minutes, maintaining a pressure of 0.1 MPa. Raise the temperature to 50℃, stir at 500 rpm for 50 minutes, and simultaneously apply 200W intermittent ultrasonic treatment for 20 minutes, working for 30 seconds and pausing for 10 seconds. Insert the ultrasonic probe 2 cm below the liquid surface. During stirring, ensure that a stable vortex forms on the liquid surface, with a vortex depth of 1 / 5 of the liquid surface height, to obtain a clear and transparent premixed base liquid.

[0037] S2: Preparation of nano-thermal conductive particle dispersion. One part of polydopamine-chitosan composite coated modified magnetic boron nitride nanosheets was added to the premixed base liquid in step S1. The temperature of the reactor was adjusted to 40℃, and a high-shear disperser was started. The dispersion was sheared at 10,000 rpm for 30 min. At the same time, 350W ultrasonic-assisted dispersion was applied with an ultrasonic frequency of 20kHz and an amplitude of 50%. The system status was observed every 5 min during the dispersion process to ensure that there was no obvious particle agglomeration. Finally, a nano-thermal conductive particle dispersion with no obvious sedimentation was obtained.

[0038] S3: Preparation of Stable Dispersion. Add 0.6 parts of polymethyl methacrylate-polyethylene glycol block copolymer and 0.2 parts of modified montmorillonite to the dispersion from step S2. Heat to 45℃ and stir at 600 rpm for 60 min. During this time, observe the liquid every 15 min using a glass rod to ensure the system is homogeneous and free of stratification. Then transfer the mixture to an S400 three-roll mill. Preheat the mixture to 50℃ before milling. The milling rollers are made of zirconia ceramic. Set the milling roller speed ratio to 3:1:5: 20 rpm for the front roller, 60 rpm for the middle roller, and 100 rpm for the rear roller, with a milling gap of 5 μm. Repeat the milling process three times. After each milling cycle, take a sample and use a laser particle size analyzer to check the particle size, ensuring D90 ≤ 2 μm. If the standard is not met, add one more milling cycle to obtain the final stable dispersion.

[0039] S4: Mixing of functional additives. Add 3 parts of graphene quantum dot-doped n-octadecane@polyurea-polyacrylate double-shell hollow phase change microcapsules, 0.2 parts of antioxidant, 0.2 parts of corrosion inhibitor, 0.1 parts of antibacterial agent, and 0.2 parts of anti-hydrolysis agent to the stable dispersion in step S3 in sequence. Adjust the temperature to 38°C and stir at 550 rpm for 80 min. Take samples every 20 min during the process and observe the dispersion uniformity through an optical microscope to ensure that there is no obvious agglomeration of functional additives.

[0040] S5: Homogenization, Aging, and Filtration. The mixture from step S4 is passed into an AH-BASIC high-pressure homogenizer. The homogenizing valve is made of tungsten carbide, and the inlet temperature is controlled at 30℃. Homogenization is performed twice at 70MPa pressure, 6 minutes each time, with the outlet temperature strictly controlled not to exceed 45℃. After homogenization, the mixture is transferred to a 28℃ constant temperature chamber for 20 hours of static aging. During aging, the mixture is stirred at 250rpm for 12 minutes every 6 hours to prevent component sedimentation. Finally, it is vacuum filtered through a 5μm polytetrafluoroethylene filter membrane at a vacuum level of 0.08MPa to remove large particulate impurities from the system, yielding the finished cooling medium. This product is then sealed in a polyethylene drum under nitrogen and stored away from light.

[0041] Example 3 (a) Formula composition (parts by weight) 70 parts of bio-based polyα-olefin-polycaprolactone block copolymer, 30 parts of polyethylene glycol monomethyl ether, 5 parts of polydopamine-chitosan composite coating modified magnetic boron nitride nanosheets, 7 parts of graphene quantum dot doped n-octadecane@polyurea-polyacrylate double-shell hollow phase change microcapsules, 1 part of polymethyl methacrylate-polyethylene glycol block copolymer, 0.6 parts of hexadecyltrimethylammonium chloride modified montmorillonite, 0.6 parts of antioxidant 2,6-di-tert-butyl-p-cresol, 0.2 parts of corrosion inhibitor benzotriazole, 0.1 parts of antibacterial agent isothiazolinone, and 0.2 parts of antihydrolysis agent polycarbodiimide.

[0042] (II) Preparation steps S1: Preparation of Premixed Base Solution Weigh 70 parts of bio-based polyα-olefin-polycaprolactone block copolymer and 30 parts of polyethylene glycol monomethyl ether, and add them to a 5L reactor equipped with an anchor-type stirrer (the stirrer diameter is 2 / 3 of the reactor's inner diameter). The reactor is equipped with a stirrer and an ultrasonic device. After sealing the reactor, purge with nitrogen three times, each time for 10 minutes, maintaining a pressure of 0.1 MPa. Raise the temperature to 50℃, stir at 500 rpm for 50 minutes, and simultaneously apply 200W intermittent ultrasonic treatment for 20 minutes, working for 30 seconds and pausing for 10 seconds. Insert the ultrasonic probe 2 cm below the liquid surface. During stirring, ensure that a stable vortex forms on the liquid surface, with a vortex depth of 1 / 5 of the liquid surface height, to obtain a clear and transparent premixed base solution.

[0043] S2: Preparation of nano-thermal conductive particle dispersion. Five parts of polydopamine-chitosan composite coated modified magnetic boron nitride nanosheets were added to the premixed base liquid in step S1. The temperature of the reactor was adjusted to 40℃, and a high-shear disperser was started. The disperser was sheared at 10,000 rpm for 30 min. At the same time, 350W ultrasonic-assisted dispersion was applied with an ultrasonic frequency of 20kHz and an amplitude of 50%. The system status was observed every 5 min during the dispersion process to ensure that there was no obvious particle agglomeration. Finally, a nano-thermal conductive particle dispersion with no obvious sedimentation was obtained.

[0044] S3: Preparation of Stable Dispersion. Add 1 part of polymethyl methacrylate-polyethylene glycol block copolymer and 0.6 parts of modified montmorillonite to the dispersion from step S2. Heat to 45℃ and stir at 600 rpm for 60 min. During this time, observe the liquid every 15 min using a glass rod to ensure the system is homogeneous and free of stratification. Then transfer the mixture to an S400 three-roll mill. Preheat the mixture to 50℃ before milling. The milling rollers are made of zirconia ceramic. Set the milling roller speed ratio to 3:1:5: 20 rpm for the front roller, 60 rpm for the middle roller, and 100 rpm for the rear roller, with a milling gap of 5 μm. Repeat the milling process three times. After each milling cycle, take a sample and use a laser particle size analyzer to check the particle size, ensuring D90 ≤ 2 μm. If the standard is not met, add one more milling cycle to obtain the final stable dispersion.

[0045] S4: Mixing of functional additives. 7 parts of graphene quantum dot-doped n-octadecane@polyurea-polyacrylate double-shell hollow phase change microcapsules, 0.6 parts of antioxidant, 0.2 parts of corrosion inhibitor, 0.1 parts of antibacterial agent, and 0.2 parts of anti-hydrolysis agent were added sequentially to the stable dispersion in step S3. The temperature was adjusted to 38℃, and the mixture was stirred at 550 rpm for 80 min. Samples were taken every 20 min during the process, and the dispersion uniformity was observed using an optical microscope to ensure that there was no obvious agglomeration of functional additives.

[0046] S5: Homogenization, Aging, and Filtration. The mixture from step S4 is passed into an AH-BASIC high-pressure homogenizer. The homogenizing valve is made of tungsten carbide, and the inlet temperature is controlled at 30℃. Homogenization is performed twice at 70MPa pressure, 6 minutes each time, with the outlet temperature strictly controlled not to exceed 45℃. After homogenization, the mixture is transferred to a 28℃ constant temperature chamber for 20 hours of static aging. During aging, the mixture is stirred at 250rpm for 12 minutes every 6 hours to prevent component sedimentation. Finally, it is vacuum filtered through a 5μm polytetrafluoroethylene filter membrane at a vacuum level of 0.08MPa to remove large particulate impurities from the system, yielding the finished cooling medium. This product is then sealed in a polyethylene drum under nitrogen and stored away from light.

[0047] Comparative Example (a) Formula composition (parts by weight) 75 parts of No. 50 mineral oil, 20 parts of polyethylene glycol monomethyl ether, 3 parts of unmodified boron nitride nanosheets, 5 parts of n-octadecane, 0.8 parts of dispersant Tween 80, 0.4 parts of antioxidant 2,6-di-tert-butyl-p-cresol, and 0.2 parts of corrosion inhibitor benzotriazole.

[0048] (II) Preparation steps Weigh 75 parts of No. 50 mineral oil and 20 parts of polyethylene glycol monomethyl ether, add them to a 5L reactor equipped with a stirrer, and stir at 400 rpm for 30 minutes at 50°C until they are evenly mixed.

[0049] Add 3 parts of unmodified boron nitride nanosheets and 0.8 parts of Tween 80, start a high shear disperser, disperse at 8000 rpm for 30 min, and simultaneously apply 200W ultrasonic treatment for 20 min to obtain a mixture.

[0050] Add 5 parts n-octadecane, 0.4 parts antioxidant, and 0.2 parts corrosion inhibitor, adjust the temperature to 38°C, and stir at 500 rpm for 60 minutes.

[0051] The mixture was transferred to a three-roll mill and milled twice with a milling gap of 10 μm and a speed ratio of 2:1:4. Then it was passed into a high-pressure homogenizer and homogenized once at a pressure of 50 MPa for 8 minutes each time.

[0052] Large particulate impurities are removed by filtration through a 10μm filter membrane to obtain a comparative cooling medium, which is then stored in a sealed container under standard conditions.

[0053] The core functionalities of the embodiments and comparative examples are compared in the table below: Table 1 The long-term stability and environmental and economic benefits of the examples and comparative examples are compared in the table below: Table 2 The data in the table show that the cooling media of Examples 1-3 of this invention are significantly superior to the comparative examples in terms of core functions, long-term stability, environmental friendliness, and economy. In terms of core functions, the thermal conductivity of the embodiment is much higher than that of the comparative example, the phase change heat storage density is greatly improved, the dispersion stability is excellent, the viscosity at 40℃ is lower, the low-temperature fluidity at -20℃ is better, and the leakage rate of the phase change core material is extremely low. In terms of long-term use and environmental protection, the embodiment shows little change in acid value after aging, low metal corrosion rate, antibacterial rate as high as 98.5%-99.5%, biodegradation rate far exceeding that of the comparative example, continuous service life more than twice that of the comparative example, significantly reduced annual maintenance cost, and better hydrolytic stability, fully demonstrating the superior comprehensive performance of the cooling medium of this invention.

[0054] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A cooling medium for data centers, characterized in that, It is composed of the following components in parts by weight: 50-70 parts of bio-based polyα-olefin-polycaprolactone block copolymer, 20-30 parts of polyethylene glycol monomethyl ether, 1-5 parts of polydopamine-chitosan composite coating modified magnetic boron nitride nanosheets, 3-7 parts of graphene quantum dot doped n-octadecane@polyurea-polyacrylate double-shell hollow phase change microcapsules, 0.6-1 part of polymethyl methacrylate-polyethylene glycol block copolymer, 0.2-0.6 parts of hexadecyltrimethylammonium chloride modified montmorillonite, 0.2-0.6 parts of antioxidant 2,6-di-tert-butyl-p-cresol, 0.2 parts of corrosion inhibitor benzotriazole, 0.1 parts of antibacterial agent isothiazolinone, and 0.2 parts of antihydrolysis agent polycarbodiimide; The bio-based polyalphaolefin-polycaprolactone block copolymer was prepared by catalytic ring-opening polymerization of caprolactone at 130°C using hydroxyl-terminated bio-based polyalphaolefin as an initiator and stannous octoate as a catalyst. The magnetically loaded boron nitride nanosheets modified with polydopamine-chitosan composite coating were prepared by sol-gel method using boron nitride nanosheets and iron oxide particles, and then coated with polydopamine-chitosan composite coating. The graphene quantum dot-doped n-octadecane@polyurea-polyacrylate double-shell hollow phase change microcapsules were prepared by suspension polymerization-interfacial polymerization using graphene quantum dots prepared by sodium citrate pyrolysis as thermal conductivity modifier. The modified montmorillonite was ion-exchange modified with a 5% (w / w) hexadecyltrimethylammonium chloride solution. The polymethyl methacrylate-polyethylene glycol block copolymer was prepared by atom transfer radical polymerization.

2. The cooling medium for data centers according to claim 1, characterized in that, The bio-based poly(α-olefin)-polycaprolactone block copolymer has a number-average molecular weight of 900, a poly(α-olefin) block ratio of 3:2 to polycaprolactone, a viscosity of 30 mm² / s at 40°C, and a molecular weight distribution of 1.

2. The polymerization reaction is carried out under nitrogen protection. After the reaction, unreacted monomers are removed by vacuum distillation, with the vacuum level controlled at 0.09 MPa and the temperature at 120°C. The amount of stannous octoate used is 0.5% of the total monomer mass. After cooling, a pale yellow, transparent, viscous liquid is obtained.

3. The cooling medium for data centers according to claim 1, characterized in that, The preparation process of the modified magnetically loaded boron nitride nanosheets with the polydopamine-chitosan composite coating is as follows: the magnetically loaded boron nitride nanosheets are ultrasonically dispersed in Tris-HCl buffer solution, dopamine hydrochloride is added, the pH is adjusted to 8.5, the reaction is stirred to form a polydopamine coating, then 1 wt% chitosan hydrochloride solution is added, the reaction is continued, and after completion, the nanosheets are washed with deionized water and vacuum dried; the boron nitride nanosheets have a thickness of 15 nm and a lateral dimension of 80 nm, the polydopamine-chitosan composite coating has a thickness of 5 nm, the chitosan has a degree of deacetylation of 90%, a number-average molecular weight of 20,000, a thermal conductivity of 850 W / (m·K), and a saturation magnetization of 12 emu / g.

4. The cooling medium for data centers according to claim 1, characterized in that, In the preparation of the graphene quantum dot-doped n-octadecane@polyurea-polyacrylate double-shell hollow phase change microcapsules, n-octadecane and graphene quantum dots were mixed uniformly at 50°C and 800 rpm for 30 min. The oil phase consisted of n-octadecane, graphene quantum dots, pore-forming agent and acrylate monomer. The aqueous phase was a 2.5 wt% OP-10 aqueous solution. The mass ratio of oil phase to aqueous phase was 1:

4. The suspension polymerization temperature was 70°C and the time was 2.5 hours. During interfacial polymerization, the molar ratio of hexamethylene diisocyanate to ethylenediamine was 1.2:1, and the reaction temperature was 55°C and the time was 1.5 hours.

5. The cooling medium for data centers according to claim 1, characterized in that, In the atom transfer radical polymerization of the polymethyl methacrylate-polyethylene glycol block copolymer, the initiator is ethyl α-bromoisobutyrate, the catalyst is CuBr / tris(2-dimethylaminoethyl)amine in a molar ratio of 1:2, the monomers are methyl methacrylate and polyethylene glycol monomethyl ether acrylate in a molar ratio of 3:2, the polymerization temperature is 70°C, the reaction time is 12 hours, and the product is purified by precipitation with petroleum ether and vacuum drying for 6 hours.

6. The cooling medium for data centers according to claim 1, characterized in that, The anti-hydrolysis agent, polycarbodiimide, has a number average molecular weight of 10,000, an isocyanate group content of 12%, and a viscosity of 800 mPa·s at 25°C. The antibacterial agent, isothiazolinone, is a compound of 5-chloro-2-methyl-4-isothiazolin-3-one and 2-methyl-4-isothiazolin-3-one in a mass ratio of 3:1, with an active ingredient content of 15%.

7. A method for preparing a cooling medium for a data center as described in any one of claims 1-6, characterized in that, Includes the following steps: S1: Weigh out the bio-based polyα-olefin-polycaprolactone block copolymer and polyethylene glycol monomethyl ether by weight, add them to a reactor equipped with a stirrer and an ultrasonic device, seal the reactor, and purge with nitrogen three times, each time for 10 minutes at a pressure of 0.1 MPa. Heat the reactor to 50°C, stir at 500 rpm for 50 minutes, and simultaneously apply 200W intermittent ultrasonic treatment for 20 minutes, working for 30 seconds and pausing for 10 seconds. Insert the ultrasonic probe 2 cm below the liquid surface to obtain a clear and transparent premixed base liquid. S2: Add the polydopamine-chitosan composite coating modified magnetic boron nitride nanosheets to the premixed base liquid in step S1, adjust the temperature to 40℃, and use a high shear disperser to shear at 10000rpm for 30min, while simultaneously applying 350W ultrasonic-assisted dispersion with an ultrasonic frequency of 20kHz and an amplitude of 50%, to obtain a dispersion of nano-thermal conductive particles without obvious sedimentation. S3: Add polymethyl methacrylate-polyethylene glycol block copolymer and modified montmorillonite to the dispersion in step S2, heat to 45°C, stir at 600 rpm for 60 min, then transfer to a three-roll mill (model S400). Preheat the mixture to 50°C before grinding. The grinding roller speed ratio is 3:1:5, with the front roller at 20 rpm, the middle roller at 60 rpm, and the rear roller at 100 rpm. The grinding gap is 5 μm. Grind three times in a cycle. After grinding, the particle size D90 is measured using a laser particle size analyzer and is ≤2 μm to obtain a stable dispersion. S4: Add graphene quantum dot-doped n-octadecane@polyurea-polyacrylate double-shell hollow phase change microcapsules, antioxidants, corrosion inhibitors, antibacterial agents, and antihydrolysis agents to the stable dispersion in step S3 in sequence, adjust the temperature to 38℃, stir at 550 rpm for 80 min, and take samples every 20 min to check the dispersion uniformity. S5: The mixture from step S4 is fed into a high-pressure homogenizer, model AH-BASIC, with the inlet temperature controlled at 30℃. It is homogenized twice at a pressure of 70MPa, each time for 6 minutes, and the outlet temperature does not exceed 45℃. After homogenization, it is aged in a constant temperature chamber at 28℃ for 20 hours. During the aging process, it is stirred at 250rpm for 12 minutes every 6 hours. Finally, it is vacuum filtered through a 5μm polytetrafluoroethylene filter membrane at a vacuum degree of 0.08MPa to remove large particulate impurities and obtain the cooling medium.

8. The method for preparing a cooling medium for a data center according to claim 7, characterized in that, The stirring paddle in step S1 is an anchor-type stirring paddle with a blade diameter of 2 / 3 of the inner diameter of the reactor. During the stirring process, it ensures that a stable vortex is formed on the liquid surface, and the vortex depth is 1 / 5 of the liquid surface height.

9. The method for preparing a cooling medium for a data center according to claim 7, characterized in that, The rollers of the three-roll mill in step S3 are made of zirconia ceramic. During the grinding process, the roller temperature is controlled at 40°C by circulating water. After each grinding, a sample is taken for testing. If D90 > 2μm, one more grinding cycle is added.

10. The method for preparing a cooling medium for a data center according to claim 7, characterized in that, The homogenizing valve of the high-pressure homogenizer in step S5 is made of tungsten carbide. After homogenization, the dispersion stability is tested by centrifugation sedimentation. The conditions are centrifugation at 3000 rpm for 30 minutes. The volume ratio of the supernatant is ≥98% to be qualified. The filtered cooling medium is sealed in a polyethylene barrel with nitrogen and stored in the dark.

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